The present invention relates to a multicharged ion source with a plurality of electron cyclotron resonance zones. It has numerous applications, as a function of the different kinetic energy values of the extracted ions, in the field of ion implantation, microetching and more particularly in particle accelerator equipment, used both in the scientific and medical fields. In electron cyclotron resonance sources, the ions are obtained by ionizing, within a closed enclosure of the ultra-high frequency cavity type, a gas e.g. constituted by metal vapours, by means of an electron plasma highly accelerated by electron cyclotron resonance. This resonance is obtained as a result of the combined action of a high frequency electromagnetic field injected into the enclosure containing the gas to be ionized and a magnetic field prevailing in said enclosure, whose amplitude B satisfies the following electron cyclotron resonance condition: B=f.2.pi.m/e, in which e represents the electron charge, m its mass and f the frequency of the electromagnetic field.
In this type of source, the quantity of ions which can be produced results from the competition between two processes, on the one hand the formation of the ions by electron impact on neutral atoms constituted the gap to be ionized and on the other hand the destruction of the same ions by single or multiple recombination, during a collision of the latter with a neutral atom. The latter can come from a gas which is not yet ionized or can be produced on the enclosure walls by the impact of an ion thereon.
The problem in this type of source is consequently to minimize the destruction of the ions formed, by preventing any collision thereof with a neutral atom.
In order to obviate this disadvantage, consideration has been given to the confinement within the enclosure forming the source of the ions formed, together with the electrons used for their ionization. This is brought about by producing within the enclosure a group of radial and axial, local magnetic fields, defining a so-called equimagnetic closed surface having no contact with the walls of the enclosure and on which the electron cyclotron resonance condition is satisfied. This surface forms the location of the points, where the amplitude of the local magnetic field has the same value. Such a source is described in French Pat. No. 2,485,798, filed on 13th Feb. 1980 by the present Applicant.
The nearer this equimagnetic surface to the walls of the enclosure, the greater its effectiveness, because it makes it possible to limit the volume of the neutral atoms present and consequently the neutral atom - ion collision quantity. However, there is a serious risk of this surface touching the inner walls of the enclosure and it is then preferable to use a second equimagnetic surface, whose amplitude is tuned to a frequency differing from the electromagnetic field, which automatically imposes the use of a second ultra-high frequency generator.